The invention relates generally to in-line, guided-microwave spectrometers and in particular to a mounting assembly for in-line, guided-microwave spectrometers used in food processing systems.
In-line analysis of food product in food processing systems can be accomplished accurately using guided-microwave spectrometers. For instance, in meat processing systems, fat, protein, moisture and salinity can be accurately measured in-line with this technology. In-line analysis is desirable because it substantially reduces, or can even eliminate, process downtime.
In an in-line, guided-microwave spectrometer processed food flows through a wave guide measurement chamber. A transmitting antenna contained within a dielectric window body is mounted within an antenna window in a sidewall of the measurement chamber. The transmitting antenna is typically copper. The dielectric window-body is typically a molded polymer, such as polytetrafluoroethylene (PTFE), polypropylene, or other suitable polymers. A receiving antenna, also typically copper, is contained within another dielectric window body that is mounted within a window through an opposite side of the measurement chamber. The antenna and the dielectric window bodies are mounted to stainless steel cover plates that are attached to the walls of the measurement chamber in order to mount the antenna through the windows in the measurement chamber. The backside of the cover plate includes microwave coaxial cable connectors. Coaxial cable is fed from the connectors to an electronic processor. In general, the guided-microwave spectrometer is able to determine various properties of the food product flowing through the measurement chamber in real-time based on detecting electromagnetic properties of the flowing food product.
In order for accurate, reliable operation, it is important that the electromagnetic antenna be protected from contamination. In food processing applications, pipe pressure can be as high as 500 to 1000 psi. Due to the high pressure within the measurement chamber, juices sometimes migrate along the seam between the dielectric window bodies and the wall of the measurement chamber. This negation along the seam can contaminate the region of the copper antenna which can lead to a degradation in measurement capability.
Another potential problem with in-line guided-microwave spectrometers in food processing applications relates to the need for high-pressure washdowns of the equipment in order to meet sanitary requirements. It is not uncommon during a high-pressure washdown for water supplied from a 1000-1500 psi hose to directly hit various components of the equipment, including the backside electronics of the wave guide antenna. Under such conditions, the electronics are susceptible to both mechanical damage and water damage.
The invention is a mounting assembly for the antennas of a guided-microwave spectrometer that renders the antennas more robust in sanitary or other washdown-type applications, such as food processing. More specifically, the geometry of the antenna cover plate and the geometry of the dielectric antenna window body are designed to better isolate the antenna region from leakage. This is accomplished by a configuration in which the joint between the dielectric window body and the cover plate, where adhesive is applied, is removed from an area of high pressure. In addition, a mounting assembly in accordance with the invention also preferably includes a back cover that is designed to protect the electrical components on the backside of the cover plate during high pressure washdown.
More specifically, the mounting assembly for the antennas includes an antenna cover plate that mounts to the measurement chamber over an antenna window in the wall of the chamber. The antenna cover plate has an antenna side (front side) and a connector side (back side). The antenna is mounted to the antenna cover plate such that the antenna loop extends away from the antenna side (front side) and the pair of microwave connectors are located on the connector side (back side). In accordance with the invention, the antenna cover plate includes a recess on the antenna side that surrounds the antenna loop. The dielectric window body covers the antenna loop and fits within the recess in the antenna side of the antenna cover plate. The antenna preferably resides within a longitudinal groove in a backside of the dielectric window body. The dielectric window body has a main body portion that extends away from the antenna cover plate and fits closely with in the antenna window on the wall of the measurement chamber. Thus, a side surface of the main body portion abuts the surface surrounding the window on the window opening side walls along a first seam. The dielectric window body also include an integral flange that extends peripherally outward from the main portion. The flange fits closely within the recess in the antenna side of the antenna cover plate. A peripheral edge of the flange abuts a wall in the antenna cover plate defining the perimeter of the recess in the antenna cover plate along a second seam. Adhesive is applied between the flange and the cover plate, preferably along and near the second seam. The adhesive is isolated from the food product and from high pressure leakage because the second seam is offset from the first seam between the sidewall of the main portion of the window body and the window opening sidewall. In addition, the second seam is located such that it interfaces entirely against an outer surface of the wall of the measurement chamber.
In another aspect, the backside of the antenna cover plate preferably includes a groove that entirely surrounds the pair of microwave connectors as well as holes in the cover plate for fasteners to mount the dielectric antenna window body to the cover plate. As mentioned, a back cover, preferably made of a material resistant to food process cleaning agents, covers the connector side of the cover plate. The back cover has a projecting rim from its lower circumferential edge that fits in the groove on the connector side of the plate. Preferably, an O-ring is located within the groove between the antenna cover plate and the edge of the projecting rim on the back cover. There is also preferably an opening in the back cover for the microwave cable. Conduit covers the microwave cable as it approaches the back cover and is preferably connected to the back cover using a threaded conduit connector in order to render the entire backside of the assembly water-tight even under high pressure washdown conditions.